This invention involves the coupling of flexible tubing where the wall thickness is approximately between 10% and 25% of the total cross-sectional area of the tubing. This tubing is generally used in agricultural, horticultural and landscaping applications to serve as a conduit carrying water and fluids from a source to an area of application. In this area of application, many different manufacturers vie for a limited market and thus market fitting sizes that are unique to their tubing, forcing the user to use only their fittings onto their tubing. Coupling devices thereby need to adapt too many size variations in order to work with the myriad of sizes available. Tubing sizes usually decrease as the tubing gets closer to the point of application. In carrying water from a far away source, the tubing starts with larger diameters and due to pressure loss and friction, the flow of water decreases requiring smaller and cheaper tubing to carry the required volume of water. Thus couplings are needed to be able to adapt from one size of tubing to the next. The tubing used in this application is generally made from polyethylene of varying densities and wall thicknesses.
The current state of the art coupling devices vary by how they interact with the tubing to create a firm enough hold to prevent leakage, yet soft enough not to crush the thin walls of the tubing thereby restricting flow and creating pressure loss. At low pressures, an internal barb can be used whose circumferentially related, triangularly shaped barbs are greater in diameter than the internal diameter of the tubing. But with increasing pressures, internal barbs fail to retain the tubing thereupon the barbs, developing the need for coupling devices to be used that either grab onto the end of the tubing or use the hydrostatic pressure of the water to firmly hold the tubing against a barrier preventing slippage and leakage. These two styles of coupling serve as the current state of development in coupling technology.
Those devices that grab onto the end of the tubing usually are two piece devices that contain an internal stabilizing piece either statically mounted within the coupler or is separately engaged away from the coupler. These couplers use a mechanical means to forcibly assist the inside diameter of the tubing to expand over increasingly larger diameter of barbs protruding from an inclined conical plane as the tubing advances toward a predetermine barrier. The tubing is displaced over these barbs by using the mechanical means of a device placed over the outside diameter of the tubing which engages the tubing through friction and forcibly displaces the tubing over the barbs. The mechanical means used are generally threads which also serve as a seal should any fluids escape from the end of the tubing into the device. The inclined plane serves a dual purpose of expanding the inner diameter of the tubing thus decreasing the wall thickness producing a more pliable tube to grasp onto, and allowing for a multitude of tubing sizes to be accommodated by a single device. The decreasing wall thickness makes the surface more pliable and increases the hoop tension or strength of the tubing over the barbs as the elastic properties of the tubing causes it to try to shrink back to it's original diameter securing itself over the barbs. Prior art is replete with examples of this style of coupling. U.S. Pat. No. 2,853,320 to Liebelt et al issued on Sep. 23, 1958 shows a smooth bore with an inclined plane that stretches the inner diameter of the tubing, where a coupling nut is slid over the outside diameter of the tubing, threadably engages the device forcing the thinned tubing walls into recesses, increasing the frictional forces over the surface area of the tubing, thus holding the tubing to the device. U.S. Pat. No. 5,178,423 to Combeau issued on Jan, 12, 1993, U.S. Pat. No. 4,437,689 to Goebel et al issued on Mar. 20, 1984 and U.S. Pat. No. 4,951,976 to Boelkins issued on Aug. 28, 1990 all contain similar devices whereby the inner diameter of the tubing is forced over a mandrel with an inclined plane and an external coupling device threadably attaches the tubing to the device. They differ in the construction of the barbs on the mandrel. Combeau uses a single frusto-conical portion where the inner diameter of the tubing is allowed to relax after the barb. Goebel uses a series of reversed angled barbs resembling buttress threads that dig into the soft inner diameter of the tubing while Boelkins uses at least one circumferential barbs located directly upon the inclined plane. Currently available devices sold in commercial and retail establishments for the purpose of connecting to or diverting fluids in flexible tubing for agricultural uses include those sold by industries leaders Raindrip Incorporated under the brand name of Stretch 'n Lock® and Aquarius Brands under the brand name of Power-Loc™. The problem associated with this style of device is that it is expensive to manufacture, as unscrewing molds must be used for female threaded pieces and barbs must be fully realized in order for the device to function. This part also has a separate external nut which can be become disassociated with the main part of the device rendering it useless. Assembly of the tubing and the connecting of the external nut requires multiple operations. Another disadvantage with this style of device is that flow and pressure is effected in the system as the internal barb acts as blockages to the fluid, disrupting the flow causing pressure loss. In long tubing runs, pressure loss due to internal disruptions can be significant enough to cause additional pumps or larger pumps to be installed increasing operating costs. An advantage of this style of device is that it can be used on multiple sizes of tubing.
Another style of coupler simple holds the outside diameter of the tubing is such a style akin to a Chinese finger puzzle, where radially located fingers are directed inwardly in a reverse angle, away from the entrance of the tubing into the device. Once the tubing is past the tips of the fingers, the tubing is denied retreat as the fingers act as barbs to the outside diameter of the tubing thereby preventing escape. The more force applied to remove the tubing the deeper the fingers dig into the tubing. Prior art contains examples of this style of device. U.S. Pat. No. 6,464,266 to O'Neill et al issued on Oct. 15, 2002 shows a device with multiple interrelated rings and fingers that could be made of plastic or metallic materials for various styles of tubing and applications. Patent Application 2005/0200122 to Mittersteiner et al published on Sep. 15, 2005 shows a combination of the device first described above with the external coupling nut and fingers, whereby the fingers serve as a wedge holding solely the outside diameter of the pipe while a smooth bore mandrel is placed inside of the tubing. Here the fingers serve as an inclined plane to extract mechanical advantage of the threads. U.S. Pat. No. 6,988,747 to Allen et al issued on Jan. 24, 2006 shows a complex device whereby the fingers are engaged by a base ring portion which in addition to the reverse angle of the fingers, lock the fingers in place around the outside diameter of the tubing. Rainbird Corporation's Easy Fit Compression Components combine the locking fingers of Allen '747 along with an internal mandrel that allows the device to be used with multiple tubing sizes. The problems associated with this style of device is the cost to manufacture and eventually sell to the user. These devices contain many parts and rely on sealing O-rings or wipers to prevent leakage over the outside diameter of the tubing. Increasing the number of parts only increases the probably of product failure and increases the cost to the user.
Another style of device is the compression coupling, whereby the outside of the tubing is inserted through an opening slightly smaller than the outside diameter of the tubing. The opening of the device consists of a single triangular shaped barb which is usually shaped as a right triangle, whereby the tubing is allowed to decompress after insertion past the barb. Mechanical forces of the barb against the surface of the outside diameter of the tubing hold the tubing in place and as the pressure increases in the tubing with the presence of fluid, the tubing walls are pushed against the barbs to a greater degree than at rest, increasing the holding power of the barb. This device is commonly known in the irrigation industry as compression devices, whereby the device is attached to a coupler or diverter such as a tee or elbow usually through ultrasonic or adhesive means. Compression devices can be molded into plastic housings as well. These devices can be color coded so the user can fit the proper size of tubing into the proper device. The advantage of this style of coupling device is that it is less expensive to manufacture and sell and is a self contained unit, where there aren't any additional pieces to engage or lose. The disadvantage of this device is it's inability to adapt to multiple tubing sizes.